test(codegen): lock deprecation-decorator generation on deprecated JSON Schema properties

[bokelley]

Closes #778

Adds a CI gate that asserts "deprecated": true in the JSON Schema source propagates to deprecated=True on Pydantic v2 FieldInfo through the pinned datamodel-code-generator==0.56.1 codegen pipeline.

Motivation: The expert review on adcontextprotocol/adcp#4904 (AdCP 3.1 additive-deprecate of CreateMediaBuySuccess.status / UpdateMediaBuySuccess.status) flagged that datamodel-code-generator has historically had uneven deprecated keyword support across versions — older pinned versions silently drop it. This test locks the contract so regressions are caught in CI rather than in production.

What changed:

• New tests/test_codegen_deprecation_contract.py with 4 assertions covering existing deprecated fields in the 3.0.7 schema bundle:
  • TargetingOverlay.axe_include_segment / .axe_exclude_segment (core schema class)
  • GetSignalsRequest.max_results
  • ProductFilters.required_axe_integrations
• Shared _assert_field_deprecated() helper with a failure message that points back to the codegen pin
• Commented-out block documenting the pending AdCP 3.1 anchor cases (CreateMediaBuySuccessResponse.status, UpdateMediaBuySuccessResponse.status) for easy activation after adcp#4904 schema sync

What tested:

• pytest tests/test_codegen_deprecation_contract.py — 4 passed
• pytest tests/ — 4734 passed, 1 pre-existing network test skipped (test_real_tls_handshake_still_validates_hostname in the signing conformance suite, unrelated to this change)
• ruff check — clean
• python -m mypy src/adcp/ — success, 805 source files, no issues

Pre-PR review:

• code-reviewer: approved — 2 nits fixed (duplicate docstring bullet removed, pending import updated from adcp.types.aliases to adcp.types)
• ad-tech-protocol-expert: approved after blocker fixed — corrected inaccurate comment claiming one assertion covers all four bundled schema occurrences (public TargetingOverlay resolves to the core schema class, not the structurally identical bundled variants)

Triage-managed PR. This bot does not currently iterate on
review comments or PR conversation threads (only on the source
issue). To unblock:

• Push fixup commits directly: gh pr checkout <num> →
  fix → push.
• Or re-trigger: comment /triage execute on the source
  issue.

See adcp#3121
for context.

Session: https://claude.ai/code/session_0169cPJV4qE4hxoLvkJsm2mg

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[bokelley]

Closing this draft as deferred/stale, not rejecting the underlying test contract. The PR is test-only, has a fixup commit plus stale storyboard failures, and only partially satisfies #778 by testing older 3.0.7 deprecated fields while the actual 3.1 anchor cases remain commented out. Keep #778 open and re-cut this after the 3.1 schema/codegen path is settled, ideally after the current codegen cleanup work lands.

[bokelley]

Acknowledged — closing as deferred/stale makes sense given the partial coverage and stale storyboard failures. #778 stays open; will re-cut after the 3.1 schema/codegen path settles and the current codegen cleanup work lands.

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[bokelley]

Noted. #778 stays open; this PR can be re-cut once the 3.1 schema/codegen path settles.

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Generated by Claude Code